THE SUN ANIMALCULE 139 



In any collection of Actinosphaeria there is a considerable 

 difference in size between individuals. They vary from o - 4 

 to '04 mm. in diameter. The smaller are the younger forms, 

 and in them the large vacuoles of the ectosarc form a single 

 peripheral layer, separated by thin radial walls of protoplasm. 



Fig. 29. 



Actinosphaerium Eichornii, viewed by reflected light, showing 

 the radiating pseudopodia, the lighter ectosarc, and the 

 darker central endosarc containing numerous nuclei. Two 

 contractile vacuoles are seen on the edge of the ectoplasm. 



In the larger and older forms the vacuoles of the ectosarc 

 are generally two or three layers deep. 



Even in the living animal, but more easily in one which 

 has been killed with osmic acid and stained with picrocarmine, 

 one can distinguish a number of minute spherical bodies, 

 deeply stained by picrocarmine, each of which contains a more 

 darkly stained central spot. The spherical bodies are the 

 nuclei, the central spots their nucleoli. The nuclei are always 



